WASHINGTON — Thirteen of the nation’s busiest air traffic control facilities are suffering from a shortage of air traffic controllers, a problem that demands “urgent attention,” a government watchdog told lawmakers on Tuesday.

The number fully qualified controllers are “below the minimum staffing requirements” the Federal Aviation Administration has set for the facilities, Matthew Hampton, a Department of Transportation assistant inspector general, told members of the House Transportation and Infrastructure Committee’s aviation subcommittee. He didn’t provide a list all 13, but cited facilities in New York, Dallas, Denver and Chicago as some examples.

The facilities are also under stressed because a large share of their controllers are still being trained and are not yet competent to work on their own, he said. Many of their more experienced controllers are also eligible to retire, Hampton said.

He cited several reasons for the understaffing: a lack of precision in the FAA models for estimating staffing requirements, a failure to fully utilize systems to determine optimal controller schedules, a lack of accurate and complete data on planned retirements, and poor communications between FAA headquarters and field offices.

Officials with the National Air Traffic Controllers Association, the union representing controllers, also complained that many of the busiest facilities are understaffed. Paul Rinaldi, the union’s president, described to lawmakers how difficult it can be to move an experienced controller from a lower-level facility like the Raleigh-Durham Airport to busier facilities. The head of the lower-level facility might not want to let the employee go because then that facility would be short an employee, he said. And the employee may not want to move despite higher pay to an area where the cost of living is higher, which is an especially difficult problem in New York, he said.

Additionally, it takes a controller who was doing fine at a less busy facility an additional two or three years of extra training at the new facility before the controller is capable of directing traffic without the direct supervision of a more experienced controller, he said. Even then, attrition rates are high, he said.

Trish Gilbert, the union’s vice president, said the understaffing problem is getting worse because a third of FAA’s 10,900 controllers are eligible to retire and because the failure rates of newly hired controllers are very high.

The FAA’s mandatory retirement age for controllers is 56. The agency also won’t hire new controllers older than age 31, which eliminates many air traffic controllers leaving the military, Gilbert said.

FAA officials said they are working on the problem and expect to meet their new controller hiring goals for this year.